Selecting the best split sizes

I have the Grande and I’m wondering what size split you’d recommend for wood. I’m already frustrated with the quality of the “seasoned” wood I’ve found, so I’m looking at some kiln dried options. I found some oak that’s 3.5”x3.5”x14” and wondering if that’s a good size. Obviously, if I put enough in, it will work. I realize there are a ton of variables, but are there any recommended dimensions?